Both headsets offer a single ear design to let the user hear side conversations. However, they do vary in wearing style. The M214i is a headband style that goes over the head, while the MX500i is under-the-ear Flex Grip® wearing style. The best wearing style depends on the user's personal preference. However, the MX500i is smaller and slightly more portable.
The other difference is in the microphone boom. The M214i has a noise-canceling microphone for reducing background noise. The MX500i has a WindSmart™ voice tube for reducing wind noise present in outdoor environments or created by fast motion noise.
Finally, the third difference is hearing aid compatibility (HAC). Only the M214i is HAC compliant.